Video recording system and method



6 Sheets-Sheet 1 In lnHliHlm-H June 25, 1968 R` M. DOLBY ETAL VIDEORECORDING SYSTEM AND METHOD Original Filed June 2, 1958 .fr V, S www.fuzmsemmm l. wuzwmuw W mlm. W mm xm v l. Pani. uwen? .no z w w K E Owo-P a Ja D 5.6928 M. an y ww mw\\ D 0 u@n n.058 m .5% .o w H s ambi@ankamen uEm .002mm 1 M N v N. M H umzucm @252.30 a

June 25, 1968 R M DOLBY ETAL Re. 26,412

VIDEO RECORDING SYSTEM AND METHOD 6 Sheets-Sheet 2 Original Filed June2, 1958 @m MW QQ own; .Il cosmo lr NEE llumwam uumwm. uzmm limits... l...532 .fmmt N \u .wk mQ nM. l. mwum NNDMOUWM m02... Q E uv. mmm

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HAROLD L. WALSH /NVEN T0195 TOEUEYS June 25, 1968 Rl M, DOLBY ETAL Re.26,412

VIDEO RECORDING SYSTEM AND METHOD Original Filed June 2, 1958 6Sheets-Sheet 5 v, 5 Yagma y B P/:m e I MWA r u lhll- IIN-HMH WE 1 0 l. n\m\ .FZ/a., A o; w WC MJoo wm m f Nuts.: .omo 5 P2 A 1| F152 i d 52 NwOSn.10 m L. n. m .rmuam Aw 0A y f HH x v umuaooanm B Nm OIwnP l m28 .POI-L NWDMOUNN DOE IT N. NQS? (l 9% m@ mm Q h-WI. IM- H |M-H .www mm) dwqoamomQMlmmw x .mesma v L dos N523 ll. owns mw* umwm @n waE. NM Us. v v @xiv.QE WMLOII! Nwnzn EHSS .lult QNWN Y vm` \N\ June 25, 1968 R. M DOLBY TALRe. 26,412

vxDo RECORDING SYSTEM AND METHOD 6 Sheets-Sheet 4 Original Filed June 2,1958 m IMIHIMIH wv w YUM? .c BEP/ 0 m 504m a AMW r mfc/M .M Jop MMm 0%@MHH June 25, 1968 R, M, DOLBY ETAL Re. 26,412

VIDEO RECORDING SYSTEM AND METHOD Original Filed June 2. 1958 6Sheets-Sheet 5 +V 79M :i562 l/zaz 5r 347 152 z799 I l: 304

357 PAY M. DOLBY Lou/s J. KA BELL Hon/A p0 E. MueP//Y 1s/249 HAROLDL.WAL5H INVENTORS 246 302 305 307 TIE- '2A June 25, 1968 R, M DOLBY ETALRe. 26,412

VIDEO RECORDING SYSTEM AND METHOD Original Filed June 2. 1958 6Sheets-Sheet e T RAY M, DOLBY 0l/l5 J. KABE/.L 3.58m Hon/APD E. MyW/mfOuf/Uf #Amm 1.. WALSH INVENTORS TTUF/VEYS United States Patent Ollce Re.26,412 Reissued June 25, 1968 VIDE() RECORDING SYSTEM AND METHOD Ray M.Dolby, Louis J. Kabell, Howard E. Murphy, and

Harold L. Walsh, by Ampex Corporation, Redwood City, Calif., acorporation of California, assignee Original No. 3,095,472, dated June25, 1963, Ser. No.

739,051, June 2, 1958. Application for reissue May 16,

1967, Ser. No. 664,893

1I] Claims. (Cl. 178-5.4)

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

ABSTRACT F THE DISCLOSURE A video recording system is provided whichincludes means for reducing frequency and/0r phase errors in areproduced color video signal introduced by changes in relative speedbetween a transducing head and' the recording medium daring reproducingas compared to recording. A pilot signal is recorded upon the recordingmedium simultaneously with a signal which has been modulated with thecomposite color video signal. During reproduction, the pilot signal,which possesses similar frequency and/or phase errors to those in thechrominance signal, is separated fro-m the modulated signal. The pilotsignal is then used to cancel the frequency and/or phase errors in thechrominance signal so that the chromnance signal is substantially jreeof hue error.

This invention relates generally to a video recording system and method,and more particularly to a video recording system and method suitablefor recording and reproducing color video signals.

Wide band signal intelligence such as monochrome and color video signalsmay be recorded magnetically on magnetic tape and thereafter reproducedto form the original signal. Suitable recording systems are described incopending applications Serial No. 427.138, tiled May 3, 1954, now PatentNo. 2,916,546; Serial No. 506,182, filed May 5, 1955, now Patent No.2,916,547; Serial No. 524,004. filed July 25, 1955, now Patent No.2,956,114; Serial No. 552.868, filed December 13, i955, now Patent No.2,921,990; Serial No. 614,420, filed October 8, 1956, now Patent No.2,968,682; and Serial No. 636.536, led January 28, 1957, now `Patent No.3,005,869. In general, the systems disclosed in said patents employ arelatively wide magnetic tape together with a rotating head assembly.The head assembly includes a plurality of circumferentially spacedmagnetic heads which sweep succcssively across the tape as it is drivenlengthwise to form longitudinally spaced laterally extending recordedtrack portions. Margins of the tape are erased, and sound and controlsignals are recorded thereon. The remaining laterally extending recordedtrack portions are of such length that the end part of one track at oneedge of the tape contains a recording which is a duplicate of `the endpart of the next track at the other edge of the tape.

lt is relatively dilicult to maintain the peripheral velocity of therecording heads constant. Any variations in peripheral velocity duringrecording and reproduc lion leads to phase and frequency variations inthe reproduced signal. Phase and frequency errors may also be introducedin the reproduced signal by changes in dimension of the magnetic tapedue to temperature changes, tension and the like. Further, the headassembly of a recording apparatus may wear down thereby giving adifferent peripheral velocity at the pick-up gaps of the various heads.

As is wcll known` a composite color signal includes luminance signalportions and a chrominance signal portion which is recorded as phase andamplitude modulation of a 3.58 mc, subcarrier. Any phase errorsintroduced in recording and reproducing is equivalent to phasemodulation of the output signal and may result in introduction of hueerrors in the reproduced color signal.

The color reference sub-carrier in the NTSC system is an odd multiple ofone-half of the horizontal line frcquency of the television signal toestablish a can-cclling dot interlace. Frequency and/or phase errorsintroduced `by recording and reproducing may increase the visibility ofthe color sub-carrier signal in the reproduced picture.

In the past, composite color signals have been recorded by employingapparatus capable of handling only a portion of the frequency spectrum.In such systems the luminance and chrominance signals have been recordedon separate record tracks and a portion of the luminance signal has beenrejected prior to recordation.

In order to record and reproduce a composite color signal, recordingapparatus capable of handling a relatively broad band of frequencies isrequired. Apparatus of this type has been brieily described above and isdescribed in detail in said copending applications. However, because ofthe nature of the composite color signal, apparatus of the abovecharacter capable of recording and reproducing the signal withoutintroduction of hue errors and destruction of the dot interlace isrelatively expensive to manufacture and difficult to adjust because ofthe close mechanical and electrical tolerances required.

It is an object of the present invention to provide a video recordingsystem and method in which a continuous pilot signal is combined with acomposite color signal and recorded therewith and in which thereproduced pilot signal is employed to demodulate the reproducedcomposite color signal to recover the chrominance signals.

lt is another object of the present invention to provide a recordingsystem and method in which a frequency modulated carrier recording of acomposite color signal including a pilot signal is formed and in whichthe reproduced frequency modulated carrier is dcmodulated to recover thecomposite signal and the reproduced pilot signal s employed to recoverthe chrominance signals from the reproduced composite signal.

It is a further object of the present invention to provide a recordingsystem and method in which a frequency modulated carrier recordinghaving successive track portions of a composite color signal including apilot signal is formed and in which the successive track portions arereproduced to reproduce the frequency modulated carrier and pilotsignal, said frequency modulated carrier being demodulatcd to form thecomposite signal and said pilot signal being employed to recover thechrominance signals from the reproduced composite signal.

These and other objects oi the invention will become more apparent fromthe following description when taken in conjunction with theaccompanying drawing.

Referring to the drawing:

FIGURE 1 is a block diagram schematically illustrating a video recordingand reproducing system in accordance with the present invention;

`FIGURE 2 is a plan view of a suitable tape transport assembly;

FIGURE 3 is a block diagram showing another video recording andreproducing system in accordance with the invention;

FIGURE 4 shows another video recording and reproducing system inaccordance with the invention;

FIGURE 5 shows another video recording and reproducing system inaccordance with the invention;

FIGURE 6 is a detailed circuit diagram of the divider and filteremployed in the system of FIGURE 3; and

FIGURES 7A-7B are detailed circuit diagrams of the 3 multiplier andlimiter employed in the system of FIG- URE 3.

`Referring to FIGURES 1 and 2, the magnetic tape 11 is driven lengthwisepast the transducing head assembly 12 by means of a capstan drive 13acting in conjunction with a capstan idler 14. A plurality oftransducing heads or units 16 are carried on the periphery of a disc ordrum 18 which is driven by a synchronous motor 19. Suitable guide means21 serve to cup the tape as it is drawn past the transducer units. Thus,as the transducer units sweep a circular path, the tape is in continuouspressure contact with the transducer units.

The tape 11 is supplied from a supply reel 22 and wound onto a take-upreel 23. The tape is guided past the transducing head assembly bysuitable self-aligning guide posts 24 and 26 and rollers 27 and 28. Thesupply and take-up reels may be carried on turntables in accordance withcustomary practice. Suitable motors may be provided for the turntablesassociated with the reels in accordance with customary practice.

`As previously described, one head is always in contact with the tape.The heads are connected to the electronic elements of the system by acommutator 29, schematically illustrated in FIGURES 1 and 2. Thecommutator may, for example, include slip rings con` nected to each ofthe heads and stationary brushes serving to make sliding contact withthe associated rings.

During recording of a broad band signal, the rotational velocity of thehead drum and of the capstan 13 are maintained with a specifiedrelationship. During reproduction, the relationship of rotationalvelocity of the head drum 18 and capstan 13 is maintained the same asduring recording within narrow limits. For this purpose, a controlsignal is recorded on the control track along the lower edge of the tapeby a magnetic transducing device 3l. The control signal is recorded as acontrol track during recording and during reproduction it is reproduced,amplified and used to control the relative speeds of the drum andcapstan drive in a manner to be presently described. A recording head 32serves to record the sound information on the other side margin of themagnetic tape. Sound track and control track erase heads 33 and 34 mayprecede the heads 3l and 32, respectively.

The electronic circuitry illustrated in block diagram of FIGURE 1 may bedivided into speed control circuitry and signal circuitry. For a clearunderstanding of the invention, the circuits are separately described.

A frequency source 36 provides the control frequency for the apparatusduring record and reproduce opera tions. The frequency 36 may, forexample, be 60 cycle line frequency, or it may be derived from a crystalcontrolled oscillator as desired. Frequency of the source 36 willhereinafter be assumed to be 60 cycle line frequency. This signalfrequency is applied to a multiplier 37 which serves to multiply thefrequency and to provide a higher frequency signal to the amplifier 38.In the discussion that follows, it is assumed that the multipliermultiplies by 4 whereby the frequency applied to the amplifier 38 is a240 cycle signal. The amplifier 38 is preferably a three phase poweramplifier suitable for driving the three phase synchronous motor 19. Aspreviously described, the motor 19 drives the head drum 18 which carriesthe transducing units or heads 16.

A revolving disc 39 coated half black and half white is also carried bythe motor shaft. A suitable light source 41 is focused on the disc andretiected light is received by a photocell 42. The output of thephotocell 42 is approximately a squarewave having a frequency equal tothe rotational velocity of the motor 19. For the example cited, theoutput squarewave signal will have a frequency of 240 cycles.

The output of the photocell 42 is passed through a shaper 43 and appliedto a frequency divider 44 which serves to divide down the frequency. Inthe instant Cit lll

example, the divider 44 divides by 4 to provide a 60 cycle frequency tothe filter 46. The filter 46 is preferably a band pass lter which formsan output signal of substantially sinewave form. During the recordoperation, the output of the filter 46 is applied to an amplifier 47,and the amplified signai is employed to drive the capstan drive motor4S. Thus, the capstan motor is driven at a rotational velocity which isdirectly related to the rotational velocity of the head drum 18. lnessence, the capstan is enslaved to the head drum. The tape moves apredetermined distance lengthwise during each complete revolution of thehead drum.

The output from the shaper 43 is also applied to a lter 49, to a controltrack amplifier 51 which supplies a signal to the control track recordhead 31.

During reproduction, the control signal 36 is again applied to themultiplier 37 and amplified and fed to the synchronous motor 19. Themotor drives the head drum at approximately the correct rotationalvelocity for the purpose of tracking the previously recorded transverserecord. The photocell 42 again derives a signal which is shaped andpassed through the filter 49. The signal from the filter 49 is fed to aphase comparator in the capstan servo amplifier 52. A second signal isapplied to the phase comparator from the control track amplifier 53which is connected to receive the output signal from the control trackhead during reproduction. The comparator produces a resultant signalhaving an amplitude and polarity which is a function of a phasedifference between the signals from the control track and photocell.This signal is applied through a filter to the grid of a reactance tubewhich is one of the frequency determining elements of a conventionalWein bridge oscillator. The oscillator functions nominally at the recordfrequency (in the illustrative example 60 cycle). The frequency ismodified up and down by the signal from the phase comparator. The outputsignal is fed to the amplifier 47 which drives the capstan motor andcontrols its rotational velocity. Thus, the capstan motor advances thetape a predetermined distance during each revolution of a head drumwhereby the plurality of heads 16 accurately track the record tracks.

The effect of the system described is to cause the capstan 13 to revolveduring reproduction is exactly the same relationship to the revolvingdrum 18, within narrow limits, as it did during the recording process.Once the drum is adjusted on the center of the track at the beginning ofreproduction, the system automatically holds the relationship constantand the revolving heads indefinitely trace accurately the recordedtransverse tracks. A suitable control system is described in U.S. PatentNo. 2,916,547.

As previously described, the lower portion of FIG- URE 1 includes thesignal electronic circuitry. The only connection between the signalelectronics and thc control electronics is the output filter 49 whichconnects to the switcher 61. A signal from the filter is employed tocontrol the switching from one play-back head to the next duringreproduction to form a recombined signal corresponding to the originalrecorded signal.

The record electronics can consist of suitable means for producing amodulated carrier together with suitable recording amplifier. FMrecording is preferred. although AM may be employed. Assuming the use ofFM recording, the record electronics can include a modulator 62 whichreceives the input signal and a record amplifier 63 connected to receivethe signal from the modulator. The output of the record amplifier 63 iscontinuously supplied to the individual head amplifiers 6669. Duringrecording, the switch 71 is positioned to connect the heads 1-4 to theamplifiers 66-69.

As described above, it is preferable to use FM record ing. The type ofFM recording which can be used for satisfactory recording andreproduction of video images is disclosed in U.S. Patent 2,956,114 and2,921,990.

During reproduction, the switch 71 is connected whereby the output ofeach head is fed individually to its own preamplifier 72-75. Thepreamplifiers are connected to feed their output to the switcher 6l.From the switcher, a reconstructed continuous signals is fed to ademodulator 76. The switcher serves to electronically switch to theindividual outputs of the heads 1-4 as they appear at the output of theamplifiers 72-75. The switcher serves to switch sequentially as theheads sweep across the tape. The output of the amplifier is areconstructed continuous signal which corresponds to the recordedsignal. An electronic switch may be employed and may be of the typedescribed in U.S. Patent No. 2,968,692.

It is also desirable to regulate the switching time so that it occursduring the horizontal retrace of a video signal. Timing information issupplied from a separate unit called the blanking switcher 77. Theblanking switcher derives its information from the processing amplifier78 and serves to control the timing of the switcher 61 so that theswitching occurs during the backporch of the reproduced signal, wherebyminimum disturbance is introduced in the reproduced signal. Theswitching system in U.S. Patent No. 2,968,692 describes a suitableblanking switcher.

As previously described, the output of the switcher is applied todemodulator 76 which serves to form a demodulated composite signal. Thedemodulated signal is preferably applied to a processing amplifier 78which is designed to make the final output of the reproduced signalacceptable for rebroadcast or retransmission. Its main purpose is toeliminate all objectionable noise from (or in between) blanking and syncpulses; and to limit to specified peak values any noise during thepicture intergal. In addition, the processing amplifier provides meansfor correcting the video linearity, and local or remote control of bothvideo and sync levels. A processing amplifier suitable for performingthese operations is described in detail in U.S. Patent No. 3,005,869.

As previously described, variations in head drum speed, tape dimensionsand tape speed lead to frequency and phase errors in the output signal.As a result, it becomes necessary to demodulate the chrominance portionof a color video signal and then to remodulate on a sub-carrier fortransmission. In accordance with the present invention, a pilot signalis recorded on the tape simultaneously with the composite color signal.During playback, the pilot signal is recovered and employed to recoverthe color information. The frequency and pbase of the pilot signalvaries in accordance with the variations described above, and in thesame manner as the color signal. Thus, the pilot signal may be employedto demodulate the color information. The pilot frequency will vary inaccordance with variations in the color sub-carrier frequency andthereby enable faithful demodulation of the color signal.

Referring to FIGURE 1, a stable reference frequency, which as willbecome presently apparent, may be derived from the color bursts of thecolor information, is multiplied or divided to obtain a pilot signal ofsuch a frequency that it does not lie in the video band of frequencies.This signal is added to the video input in an adder 82. The combinedsignal (pilot and composite video input signals) is then employed tomodulate a carrier. The modulated carrier is amplified and recorded aspreviously described.

The reproduced signal is applied to the switcher 61 and thereconstructed combined signal is applied to a demodulator 76. The outputof the demodulator is the combined signal. This signal is applied to asplitter 83 which recovers the pilot signal and applies the same to amultiplier or divider 84 which then multiplies or divides the pilotcarrier frequency to form a 3.58 me. sub-carrier frequency. The 3.58 mc.sub-carrier is applied to the I and Q demodulator 86` The demodulatedcolor signal is applied to a processing amplifier 78. The output of theprocessing amplifier is applied to a suitable filter 87 to form the Ycomponents. The signal is also applied to a filter 88 and thence to theI and Q demodulator 86 to where the I and Q signal components of thevideo signal are recovered.

Thus it is seen that during recording a pilot signal is combined withthe video signal and recorded simultaneously therewith to formsuccessive tracks on the magnetic tape. When the signals are reproduced,the pilot signal is separated from the reproduced signal and operatedupon to derive a 3.58 mc. local frequency for application to the I and Qdemodulator 86. The local signal (derived from the pilot signal) appliedto the I and Q demodulator will have frequency and phase variationswhich correspond to the frequency and phase variations introduced by themagnetic recording apparatus. Thus, the local signal will vary inaccordance with variations in the color sub-carrier, and the I and Qdemodulator will serve to faithfully recover the I and Q information. Ifthe signal is to be retransmitted, the I and Q signals are thenremodulated onto a sub-carrier and combined with the Y signal to form acomposite color signal suitable for transmission purposes.

Another recording system employing pilot carriers is schematicallyillustrated in FIGURE 3. The block 101 represents the tape transportassembly, associated control electronics and a portion of the videoelectronics. The video signal intelligence is shown applied to an FMmodulator 62, previously described. The output of the modulator isapplied to a high pass filter 103 and thence to an adder 104. The 3.58mc. continuous carrier which may be developed from the color bursts inthe color signal in conventional manner is applied to a divider whichserves to divide down the frequency and apply the same to a filter 106.This signal serves as the pilot signal. The pilot signal is applied tothe adder 104 where it is added to the FM modulated carrier and appliedto the record amplifier.

In one particular example, the divider 104 divided the input frequencyby 4 to give an output signal frequency of 895 kc. The filter 106 was ofthe series parallel tuned type and with transmission zeros at 1.79 mc.and 3.58 mc. in order to eliminate harmonics of the pilot frequencywhich would be visible in the reproduced picture. The filter 103 was ahigh pass lter having a cut-off in the neighborhood of 1 mc. to therebyeliminate any interference of the color signal side bands with therecorded pilot signal. Thus, the recorded signal information was arecord which contained the composite video signal intelligence togetherwith the 895 kc. pilot signal recorded concurrently therewith.

It is, of course, apparent that other divisions might be employed, forexample, by 5 or any other suitable number, or that the signal might bemultiplied up, as will be presently described. However, in any one ofthese systems it is apparent that a pilot frequency is preferably chosenwhereby it does not interfere with the color signal information and viceversa.

In the embodiment of FIGURE 3, the reproduced signal, which includes thecolor signal and pilot signal, is applied to a splitter 108 which servesto separate the pilot carrier and color signal. For example, thesplitter might comprise a series parallel resonant trap which separatesthe 895 kc. signal at the switcher output. The pilot signal is appliedto a limiter 109 to reduce the amplitude of switching transients. Thesignal is then applied to a multiplier 111 which produces 3.58 mc.signal. This signal may be subjected to limiting 112 to remove anyamplitude tiuctuations that would affect the output of the unbalancedcolor demodulators. The video signal output of the splitter may beapplied to a high pass filter 113 to remove any remaining pilot signaland thence to the demodulator 76 of the type previously described. Thecomposite color signal is then operated upon by conventional videotechniques to recover the luminance and chrominance information,employing the 3.58 me. carrier derived from thc pilot signal in thecolor demodulators.

A suitable regenerative divider is illustrated in FIG- URE 6 and will bepresently described in detail. A suitable frequency multiplier 111 isshown in detail in FIG- URE 7A-B, and will be presently described indetail.

As previously described, it is preferable to choose a pilot signalhaving a frequency which lies outside the video band in order to avoidvisible effects due to the pilot signal. The pilot signal should liewithin the pass band of the transmission channel of the recordingmachine and preferably should be a simple rational multiple of the colorsub-carrier frequency in order to facilitate the performance of requiredoperations on the pilot signal. There should be no visible effects fromthe intermodulation product of the pilot signal and the colorsubcarrier. A 4.4 nic. pilot signal is suitable in this respect. A 4.4mc. pilot signal has a cancelling interlace beat frequency which resultsin the visibility of the beat (intermodulation product) being reduced toacceptable levels. Such a carrier system is shown in FIGURE 4. The 4.4mc. signal is generated by multiplying the 3.58 color subcarrier by lf3in a regenerative frequency divider 121. The pilot signal is added tothe color signal at the adder 122 to form a combined signal. Thecombined signal is then modulated [b ythe] by the modulator 62 andrecorded as previously described. The reproduced signal is applied tothe demodulator 76 and the combined signal is then operated upon by astripper 122 to recover the color signal 123. The color signal isapplied to the processing amplifier. The pilot signal is applied to anon-ambiguous divider 124 which multiplies by Vn to form a 3.58 mc.signal. The color signal is then demodulatcd as previously described.

Referring to FIGURE 5, another system for recording and reproducing acolor television signal including a pilot signal is illustrated. A bursttakeoff and oscillator 126 is employed to form a 3.58 mc. subscarrier.The color sub-carrier is applied to a divider 127 and thence to an added128. The pilot signal is handled as part of the video signal and isapplied to the modulator 62 and recorded by the tape recorder 101. Thesignal is reproduced and demodulated by demodulator 76. The demodulatedsignal is applied to a band pass amplifier and then to a limiter 128 toremove amplitude modulation caused by video frequencies in the vicinityof the pilot frequency'. The resulting signal is converted to a sinewavein the pilot tone remover 129 and combined with the demodulated signalin opposite polarity with respect thereto so as to cancel out the pilotsignal leaving the video signal at the output. The pilot signal is alsoapplied to a multiplier 131 which serves to multiply the frequency up togive a 3.58 me. color sub-carrier. As previously, described, this signalis employed to demodulate the color sub-carrier. In one particularexample, the divider 127 divided by 2 gives a 1.79 megacycle signalwhich was then combined with the video and the signals treated as partof the video signal. The band pass amplifier was such as to pass anarrow band of frequency around 1.79 megacycle.

It is to be observed with respect to the system of FIG- URE that a notchfilter might be employed for removing the pilot signal rather than thesystem described. If a notch filter is employed, the pilot tone removermay not be necessary.

Referring to FIGURE 6, a suitable divider for dividing the 3.58 signalby 4 together with output filters is illustrated. Referring to thefigure, the vacuum tubes 136 and 137 and associated circuit elementsform a regenerative divider. The input signal is capacitively coupled tothe grid of the tube 136. A tuned circuit 138 is disposed in the platecircuit and is tuned to a frequency of 895 kc. The tuned circuit iscoupled to the grid of the tube 137 by a suitable transformer 139. Thus,the tube 137 has a signal frequency of 895 kc. applied to its grid. Atuned circuit 141 is disposed in the plate circuit of the tube 137 andis tuned to the third harmonic or 2.685 mc. This circuit is connected tothe third grid of the mixer tube 136. Thus, there is a mixing of thesignals in the tube to form upper and lower side bands. The tunedcircuit 138 is tuned to the lower side bands. The signal coupled fromthe tuned circuit 138 is also applied to the grid of the tube 143 whichis connected as a cathode follower. The inductor 144, the tuned circuit146 and the capacitor 147 seve to filter out any of the 1.19 mc. and3.58 mc. frequencies as previously describcd. The filtered output of thecathode follower is applied to the line 148 where it is combined withthe output of the filter 103 (FIGS. 3 and 6) and applied to the recorderalong the line 149.

Referring to FIGURES 7A-B, a suitable frequency multiplier for areproduce channel is illustrated. The input includes a series parallelfilter network including the sections 151 and 152. respectively, whichserve to separate the pilot signal from the video signal. The videosignal is then applied to the demodulator as previously described andthe pilot signal is applied to an amplifier stage including the tube153. The amplified signal is applied to a pair of diodes which form alimiter 154 lo reduce the amplitude of the switching transients. Theoutput of the limiter is capacitivcly coupled to the tube 156 which isconnected in circuit to form one stage of a two-stage amplifier with thetube 157 forming the sccond stage. The output of the amplifier' isapplied to the primary of a transformer 158 whose secondary is connectedas a full wave rectifier circuit 159 which acts as a frequency doublerwhereby the frequency on the line 161 is double the input frequency. Thesignal from the frequency doubler is applied to an amplifier stageincluding the tube 162 and applied to another frequency doubler whichcomprises a transformer 163 having its secondary connected to a fullwave rectifier 164. The resultant frequency is then four times the inputfrequency or 3.58 inc. The output is then amplified in the amplifierincluding the tube 167, limited by the limiter 168, amplified by theamplifier including the tube 169, limited by the limiter 1.71, amplifiedby the tube 172. and coupled by by trausformer 173 to an amplifierincluding the tube 174.

Apparatus was constructed in accordance with the foregoing in which thevarious elements in the frequency divider and multiplier had thefollowing values, and in which the complete recording system was of thetype described with respect to FIGURES l, 2 and 3:

Voltages |V=250 volts Tubes 136 6BE6 162 6AU6 .137 6AU6 167 6AU6 143 6C4169 6AU6 153 6AG5 172 6AU6 156 6AG5 174 6AQ5 157 6AG5 Transformers 139,primary 15T, secondary 7T 158, primary 12T, secondary 12T 163, primary8T, secondary 8T 173, primary 8T, secondary 8T Capacitors 147 mmf 3000217 mmf 200 181 mmf 51 218 mf-- .0l 182 mmf 100 219 mmf 5l() 183 mmf 510221 mf .0047 184 mf .l 222 mmf 50-40() V186 mmf 50-40() 223 mmf 1U() 187mmf 51 224 mf .0022 188 mmf 100 226 mmf 5l() 189 mmf 100 227 mf-- .0022191 mf .01 228 mmf 30 Capacitors 192 mmf-- 100 229 mmf 510 193 mf-- .001231 mmf 510 194 mmf 750 1232 mf-- .0022 196 mmf 150 233 rmnf 510 197mmf-- 150 234 mf-- .0022 198 mf .01 236 mf-- .01 199 mf .01 237 mmf--510 201 mmf 500 238 mf 30 202 mf 0.1 239 mmf" 510 203 mmf-- 250 241 mf.01 204 mmf 510 242 mf .0022 206 mmf 510 243 mmf" 510 207 mf .0l 244 mf.0022 208 mi-- 0047 246 mmf 50-400 209 mf 0.1 247 mmf 100 211 mf .01 248mmf" 510 212 mmf-- 510 249 mf .0l 213 mmf 50-400 251 mmf 120 214 mmf 200252 mmf 1100 216 mf .01 253 mL- .0022

Resistors 261 ohms 1K 303 ohms 100K 262 do 2K 304 do 2K 263 do 20K 306do 13K 264 do 75 307 do 430 266 do 24K 308 do 68K 267 do 20K 309 do 15K268 do 100K 311 do 1K 269 do 12K 312 do 10K 271 do 68K 313 do 100K 272do 100K 314 do 13K 273 do 1K 315 do 400 274 do 680 316 do 58K 275 do 24317 do 2K 276 do 300 318 megohms-- 2.4 277 do 5.1K 319 do 1.2 278 do 75320 do 2.4 279 do 15K 321 ohms 10K 281 do 260 322 do 13K 282 do 68K 323do 430 283 do 2K 324 do 2K 284 do 4.7K 326 do 68K 286 megohms 72 327megohms-- 2.4 287 do 2.4 328 do 1.2 288 do 2.4 329 do 2.4 289 ohms-- K330 ohms 10K 291 do 15K 331 do 2K 292 do 360 332 do 13K 293 do 68K 333do 480 294 do 2K 334 do 68 296 do 12K 336 do 100K 297 do 15K 337 do 80K298 do 360 338 do 2K 299 do 68K 339 do 2K 301 do 1K 341 do 270 302 do12K Inductors 144 mh-- 2.7 346 rnh 3.4-7 342 do 13.0 347 do 3.4-7 343 do35.0 348 do 66 344 do 11 349 do 66 Diodes 351 IN68 357 1N100 352 IN68358 IN68 353 IN100 359 IN68 354 IN100 361 IN68 356 IN100 362 IN68Apparatus constructed in accordance with the foregoing was operated anda video signal was successfully recorded, reproduced and the colorsub-carrier demodu- 10 lated to form Y, I and Q signals free of huedistortions and having suitable dot interlace.

Thus, it is seen that an improved video tape recording and reproducingsystem is provided. The system is capable of recording and reproducingcolor video signals without the introduction of distortion due tofrequency and phase variations introduced by the magnetic tape recording and reproducing process.

We claim:

1. A magnetic recording system wherein a composite color video signal,including a color burst signal, is recorded on a magnetic medium and issubject to frequency and phase errors comprising:

means for deriving the color burst signal from the video signal duringthe record mode;

means for transforming the frequency of the burst signal to a frequencyoutside the band of the color video signal to be recorded, thetransformed signal providing a pilot signal;

means for providing a carrier signal;

means for adding the composite video signal and the pilot signal;

means for modulating the carrier signal with the added signal;

and means for amplifying and recording the modulated signal on trackportions of the magnetic medium.

2. A magnetic recording system wherein a composite color video signal,including a Color burst signal, is recorded on a magnetic medium and issubject to frequency and phase errors comprising: means for deriving thecolor burst signal from the video signal during the record mode; [meansfor transforming the frequency of the burst Signal to a frequencyoutside the band of the color video signal to he recorded, thetransformed signal providing a pilot signal',] means for providing acarrier signal; means for frequency modulating the carrier signal withthe color video signal; means for transforming the frequency of theburst signal to a frequency below the band of the frequency modulatedcarrier signal to be recorded, the transformed signal providing a pilotsignal; means for adding the modulated carrier signal and the pilotsignal; and means for amplifying and recording the added signal on trackportions of the magnetic medium.

3. A magnetic reproducing system wherein a modulated composite colorvideo signal and a pilot signal related to a color burst signal are tobe reproduced from a recorded magnetic medium, such signals beingsubject to frequency and phase errors during the record mode comprising:means for deriving the recorded signal including the composite signaland the pilot signal` both having the same frequency and phase errors;means for demodulating the derived signal; means for separating thepilot signal from the demodulated video signal; means for transformingthe separated pilot signal to a signal having a frequency substantiallythe same as that of the color burst signal; and means for applying thetransformed separated pilot signal to a chrominance demodulatorsimultaneously with the demodulated video signal for obtaining thechrominance components of the reproduced color signal, and forcorrecting for the frequency and phase errors experienced during therecord mode.

4. A magnetic reproducing system wherein a modulated composite colorvideo signal having luminance and chrominance I and Q components, and apilot signal related t0 a color burst signal are to be reproduced from arecorded magnetic medium, such signals being subject to frequency andphase errors during the record mode comprising: means for deriving therecorded signal including the composite signal and the pilot signal,both having the same frequency and phase errors; means for demodulatingthe derived signals; means for separating the pilot signal from thedemodulated color video signal; means for filtering the luminancecomponent from the demodulated signal; means for transforming theseparated pilot signal to a signal having a frequency substantially thesame as that of the color burst signal; and means for applying thetransformed separated pilot signal to an I and Q demodulatorsimultaneously with the de modulated video signal for obtaining the Iand Q components of the reproduced color signal, and for correcting forthe frequency and phase errors experienced during the record mode.

5. A magnetic recording and reproducing system wherein :i compositecolor video signal including a color horst signal is recorded andreproduced, and wherein such :ignnls are recorded on a magnetic mediumand are subject to frequency and phase errors comprising: means lorderiving the color burst signal from the video signal during the recordmode; [means for transforming the frequency of the burst signal to afrequency outside the band of the color video signal to be recorded, thetransformed signal providing a pilot signah] means for providing acarrier signal; means for frequency modulating the carrier signal withthe color video signal; means for transforming the frequency of theburst signal to a frequency below the baud of the frequency modulatedcuri-ier signal to be recorded, the transformed signals providing apilot signal; means for adding the modulated signal and the pilotsignal; trneans for amplifying und recording the added signal on singletrack portions of the magnetic medium; means for deriving the recordedsignal having frequency and phase errors during the playback mode; menusfor separating the pilot signal having the same frequency and phaseerrors as the recorded signal from the derived recorded signal; meansfor demodulating the derived composite video signal [including the pilotsignal; means for separating the pilot signal having the same frequencyand phase errors as the recorded signal from the demodnlated videosi'rnnl means for transform- Z1 ing the separated pilot signal to asignal having a frequency substantially the same as that of the colorburst signal; and means for applying the transformed separate pilotsignal to a demodulator in conjunction with the de modulation videosignal for demodulating the chromi nance components of the reproducedsignal, and for Cor rceting for the frequency and phase errors.

6. Apparatus in accordance with claim 2 which further includes areproducing system comprising.' means for deriving the recorded signalincluding the frequency modulated carrier signal and the pilot signal,both hurling the sume frequency and phase errors; means for separatingthe pilot signal from the frequency modulated carrier signal; means fortransforming the separated pilot signal to a signal having a frequencysubstantially the same as that of the color burst signal; means fordemodulating the frequency modulated carrier signal, and means receivingthc chrominauce portion of said demoduloted signal und said transformedpilot signal for providing at its output the chrominance portionsubstantially free of hue errors caused during the record mode.

7. Apparatus in accordance with claim 1 which further includes areproducing system comprising.' means for deriving the recorded signalincluding the carrier signal modulated with the composite video signaland the pilot signal both having the sume frequency and phase errors;means for demodulating the derived signal; means for separating thepilot signal from the demodulated color i'idco signftl; mcd/ts fortransforming the separated pilot signal to it signal having a frequencysubstantially the sinne as that of the color burst signal, and meansreceiving the transformed separated pilot signal and the denrodnlutedcolor video signal for correcting the frequency und phase errors in thechrominance portion of the demoduluted color video signal experiencedduring the record mode.

8. Apparatus in accordance with claim l wherein said frequencytransforming means comprises a frequency multiplier providing atransformed signal of higher frequency than the burst signal.

9, Apparatus in accordance n'tlz claim 6 which further includes achrominance lter for separating the chrominance portion from saiddemoclulated video signal before introduction of the chrominancc portioninto said las! mentioned means, and means for combining the chrominunceportion at the output of said last mentioned means and the remainder ofsaid demodulated video signal.

li). Apparatus in accordance with Claim 5 which further includes achrominance filter for separating the chrominance components from saiddemodulnted video signal before intrrnluction of the clu'ominance signalinto said demodulator.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 2,028,232 1/1936 Miller. 2,816,162 12/1957Johnson. 2,823,255 2/1958 Hall. 2,892,017 6/1959 Houghton. 2,892,022 6/1959 Houghton. 2,909,596 10/ 1959 Fay. 2,921,976 1/ 1960 Johnson.2,954,441 9/1960 Anderson. 2,960,563 1 1/1960 Anderson. 2,979,558 3/1961Leyton. 3,019,291 1/1962 Houghton.

ROBERT L. GRIFFIN, Primary Examiner. HOWARD W. BRITTON, AssistantExaminer.

